Patent GB-190326849-A (GB)
Title: Telephone Systems
Inventor: FAIRWEATHER WALLACE
Filed: 1903-12-08
Granted: 1904-03-17
Abstract: 26,849. Fairweather, W., [Stromberg Carlson Telephone Manufacturing Co.]. Dec. 8. Telephone systems; telephone calls.-Relates to a party line telephone system in which the subscribers are divided into two groups, connected to the line in two ways, the one group p using the complete metallic circuit, and the other group using the line wires in parallel, with an earth return. The two sides of the line 17 are bridged at the exchange by an impedance coil 23, which offers such a high impedance to currents passing through its coils in series as to prevent short-circuiting of the line when the metallic circuit is used, but presents little impedance to currents passing through its coils in parallel to the conductor 34. The party line is connected to two jacks 10, 11 at the exchange, the jack 10 being used for metallic circuit working, and the jack 11 for the earth return. Of the four subscribers A, B, C, D on the line, A, B normally use the earth return, and C, D the metallic circuit, but switches are provided for enabling each subscriber to use the line in either manner. The call bells 6 at the subscribers' stations are polarized, so that selective calls can be made by the use of currents in opposite directions, but the signal bells 18, 19 at the exchange are not polarized, one or other being sounded according as the calling current is sent through the metallic circuit or otherwise. In consequence, if subscriber A rings up subscriber B directly, which he can do by manipulating his reversing-key 26 so that the unidirectional current generator 7 sends its current in the proper direction, he must also ring up the exchange, but it is arranged that a single stroke of the exchange call-bell is disregarded by the operator, as indicating merely a call between two subscribers on that line. The ringing circuit between A, B comprises the conductor 24, one side of the reversing-key 26, the corresponding side of the circuitchanging key 30, impedance coil 21, the line wires 17<1>, 17<11> in parallel, conductors 50, impedance coil 22, and bell 6 to earth, returning by the conductors 37. 38 and the keys 30, 26 to the generator. By manipulating the circuit-changing key 30, subscriber A can call up subscriber C or D according to the direction of the current sent, the key serving to cut out the impedance coil 21 and the earth connection, and to connect the generator across the metallic circuit. Similarly, subscriber C can call up subscriber A or B by manipulating the circuit-changing key 30, in which case a special differential winding on the bell 6, serving as the equivalent of the impedance coil 21, is introduced into the circuit, the ringing or speaking currents dividing at the point 46 and passing to the lines 17', 17<11> in parallel. At the same time, the necessary earth connection is made at 64. Associated with the operators' cord circuit is a listening key 14 and a unidirectional current generator 16 with reversing key 15. By inserting the calling plug 12<1> in one or other of the jacks 10, 11 and suitably manipulating the reversing- key, any one of the four subscribers on a party line can be called up from the exchange. Two subscribers, one from each group (or from the same group if a circuit-changing key is actuated) can speak through the exchange simultaneously, owing to the different characters of the circuits used. In a modification, polarized bells are used at the subscribers stations with the usual automatic make-and-break device so as to ring continuously, instead of giving a single stroke only. The signal bells may be replaced by visual indicators.